Control systems for precise operation of mechanisms such as machine tools, industrial robots and the like are usually electrical or hydraulic. Both types are expensive and use bulky and heavy motors and actuators and much wiring or tubing capable of carrying considerable power or hydraulic pressure. In large machine tools the weight is not critical, but on any moving apparatus where the power drive or structure becomes part of the load, such as a jointed arm robot, any excess weight on the moving components adds to the load that must be moved and this increases the power requirements, and thus the cost.
Both electrical and hydraulic mechanisms are capable of accurate positioning over reasonable distances and are used extensively in numerically controlled machines, but both have limitations in small and precise motions and distances. This is due primarily to static friction in the various mechanisms that must be overcome each time a mechanism is moved. Power must build up to a particular point at which the static friction is broken and the mechanism will move. In making very small movements the resultant jerk and inertia of the moving parts can make it difficult to stop at a precise position. In electrical and some hydraulic systems a dithering technique has been used in which a constant dithering signal is applied to the moving parts to keep them in constant infinitesimal motion to continuously break the static friction. In many instances, however, this is undesirable and impractical.
Pneumatic power systems are much lighter and simpler and considerably lower in cost than equivalent hydraulic or electrical systems, but are usually not considered suitable for precise servoed machine control due to the compressibility and cushioning effect of air as a driving medium. A pneumatic power system would make it possible to greatly reduce the weight, complexity and cost of industrial robots in particular and power actuated machinery in general.